Magnetic switching devices comprising ni-mo-fe alloy

ABSTRACT

A new family of magnetic alloys containing small amounts of Zr or Be has been developed primarily for use in memories and coincident current switches. These alloys are of particular utility in those applications requiring a terminal heat treatment since they can be optimized to be square looped and essentially nonmagnetostrictive in the heat treated state with coercivities in the range 0.2-3 oersteds. One member of this family, developed for use as the soft magnetic material in the piggyback twistor memory element, has the composition; 80.2 percent nickel, 5.65 percent molybdenum, 0.25 percent zirconium and 0.25 percent manganese.

United States Patent [1 1 Chin et a1.

1 1 MAGNETIC SWITCHING DEVICES COMPRISING NI-MO-FE ALLOY [75] Inventors:Gilbert Yukyu Chin, Berkeley Heights, N .J.-, William BrightmanGrupeniThomas Charles Tisone, both of Emmaus, Pa.

[73] Assigneei Bell Telephone Laboratories,Incorporated, Murray Hill,Berkeley Heights, NJ.

[22] Filed: Mar. 18, 1970 [21] Appl. No.: 20,597

[52] US. Cl 340/174 ZB, 75/170, 148/3155,

148/120, 340/174 NA, 340/174 TW [51] Int. Cl Gllc 11/12, C22c 19/00 [58]Field of Search 148/3155, 31.57,

148/120, 121; 75/170; 340/11.4, 166 C, 174 R, 174 EA, 174 NA, 174 QB,174 PM, 174

1 Sept. 25, 1973 1,715,541 6/1929 Elmen 148/3155 X 1,792,483 2/1931Elmen 148/3155 2,990,277 6/1961 Post et a1. 148/31.55 X

OTHER PUBLICATIONS Stanley, .1. K.; Metallurgy and Magnetism, Cleveland,1949 pp. 37, 46-49.

Primary Examiner-L. Dewayne Rutledge Assistant ExaminerW. R. SatterfieldAtt0rneyW. L. Keefauver [57] ABSTRACT A new family of magnetic alloyscontaining small amounts of Zr or Be has been developed primarily foruse in memories and coincident current switches. These alloys are ofparticular utility in those applications requiring a terminal heattreatment since they can be optimized to be square looped andessentially nonmagnetostrictive in the heat treated state withcoercivities in the range 0.2-3 oersteds. One member of this family,developed for use as the soft magnetic material in the piggyback twistormemory element, has the composition; 80.2 percent nickel, 5.65 percentmolybdenum, 0.25 percent zirconium and 0.25 percent manganese.

1 Claim, 6 Drawing Figures PATENTEU 3; 78 1.904

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G. K CHIN lA/VENTORSZ'W. B. GRUPEN TI 6'. TISO E ATTOR EV MAGNETICSWITCHING DEVICES COMPRISING NI-MO-FE ALLOY BACKGROUND OF THEINVENTION 1. Field of the Invention The invention is in the field ofmagnetic alloys intended for use in memories and to perform more generalswitching operations.

2. Description of the Prior Art A bit of information is stored in amagnetic memory as the direction of remanent magnetization in one of themagnetic elements contained within the memory. The usual operation isbinary in which there are two possible remanent states. A signal is readout of the memory when the remanent state is caused to reverse. Thesignal produced is proportional to the time rate of change of magneticflux during the reversal. This signal, then, is dependent upon both thetotal amount of remanent magnetization and the switching speed of theelement.

Memories generally can be classified as to the permanence of the storedinformation. In some memories, the read operation destroys the storedinformation while some memories contain means for preserving orregenerating the information for later use. One memory of the lattertype is the Piggyback Twistor Memory disclosed by W. A. Barrett, Jr. inU.S. Pat. No. 3,067,408 which issued Dec. 4, 1962. The Piggyback TwistorMemory element is formed by wrapping two strands of magnetic material,differing in remanence and coercivity, and adjacent to one another,around a single conducting core. The material possessing higherremanence and coercivity, which will be referred to as the hardmaterial, serves as the storage medium into which the information iswritten. The material with lower remanence and coercivity, which will bereferred to as the soft material, serves as the read out medium whichcan be switched without disturbing the information written into the hardmaterial. When the read switching field is removed, the remanentmagnetization of the bit of hard material restores the adjacent bit ofthe soft material to its original state so that it can be read out againwhen required. This device has been successfully fabricated and hasproven to be a useful and versatile memory. In order to extend its rangeof use, development work has continued and a new hard material withimproved properties has been developed (E. A. Nesbitt et al., Journal ofApplied Physics 39 (1968) 1268).

BRIEF DESCRIPTION OF THE INVENTION The invention disclosed here is thedevelopment of an improved soft material and suitable processingconditions for that material. It is required that this soft materialpossess its desirable properties after a terminal heat treatment stepwhich may be required to develop specific properties of the hardmaterial or to satisfy other device requirements. A family ofmolybdenumpermalloy alloys with small additions of beryllium and- /orzirconium has been found to exhibit the desired squareness, coercivityand low degree of magnetostriction after a terminal heat treatment. Onemember of this family particularly suited to a specific contemplateddevice has the composition including 80.2 percent nickel, 13.65 percentiron, 5.65 percent molybde num, and 0.25 percent zirconium. The boundsof this generally useful family together with recommended processingconditions are presented below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the Fe-Ni-Mo compositiondiagram indicating preferred composition ranges;

FIG. 2 is a plane view of a section of piggyback twistor memory wirewith the magnetic tapes partially unwrapped to show their situation;

FIG. 3 is a set of curves showing the coercivity as a function of thetemperature of the terminal heat treatment for three exemplary alloysvarying in beryllium content;

FIG. 4 is a set of curves showing the magnetostriction (expressed as thechange in coercivity for a fixed change in stress) and squareness ratioas a function of the temperature of the terminal heat treatment forthree exemplary alloys varying in beryllium content;

FIG. 5 is a set of curves showing the coercivity as a function of thetemperature of the terminal heat treatment for a number of exemplarywires varying in zirconium content and work history; and

FIG. 6 is a set of curves showing the magnetostriction (expressed as thechange in coercivity for a fixed change in stress) and squareness ratioas a function of the temperature of the terminal heat treatment for anumber of exemplary wires varying in zirconium content and work history.

DETAIL DESCRIPTION OF THE INVENTION EXEMPLARY DEVICE USE The exemplarypiggyback twistor memory wire shown in FIG. 2 is composed of strands ofa soft magnetic material 21 and a hard magnetic material 22 in the formof flat tapes wrapped around an electrically conducting wire 23. A drivecurrent in the electrical conductor 24 can be used to interrogate thememory bit by producing a magnetic field such as to cause the bit ofsoft tape to reverse its magnetization. A larger drive current inconductor 24, possibly in combination with a current passing throughconductor 23, can be used to write information into the memory bit byreversing the magnetization of the bit of hard tape. The soft tape 21 isdesirably square looped (i.e., its remanent flux (1m, should be nearlyequal to its saturation flux, in order to minimize spurious signalsduring interrogation (shuttle signals). For one proposed use it isrequired that the coercivity of the soft tape be of the order of 0.7oersteds and the squareness ratio, be greater than 0.8. However, onecould contemplate the use of coercivities from 0.2 oersteds to 3oersteds or more and many devices can tolerate less squareness. Inaddition, it is desirable that the finished device be insensitive tomechanical stress.

The hard magnetic tape 22 must have a remanent flux, da which is greaterthan the saturation flux, tb of the soft tape 21 and a coercivity, I-Imore than twice the coercivity of the soft tape 21. Then, after the softtape is switched by the interrogation signal it is switched back to itsoriginal state by the magnetization of the hard tape.

The material properties which make the disclosed alloys suitable for thetwistor use are the very same properties which are desirable for a wisevariety of other memory devices and more general switching uses.

Alloy Compositions Beryllium and/or zirconium additions in the range of0.1-1 weight percent of the total 100 percent of the other constituentsprovide control over the coercivity of this family of magnetic alloys.It is felt that this control stems from the following proposedmechanism: During heat treatment, these materials form nonmagneticintermetallic type second phase precipitate. Under suitable conditionsthe precipitate comes out of solution as particles in the size range 200A to 2,000 A. These particles are most effective in impeding thepropagation of domain walls when the particle size is roughly equal tothe thickness of the wall (typically 500 A to 1,000 A). [n the disclosedmaterials this causes a coercivity peak as the heat treatment history isvaried to produce precipitate particles through the above size range.High temperature heat treatment (greater than l,000 C) tends to drivethe precipitate back into solution and to homogenize the alloys whilelower temperature (400 l,000 C) heat treatment tends to causeprecipitation. At a given high temperature the longer the time of heattreatment the greater the homogenization. At a given low temperature thelonger the time of heat treatment the larger the precipitate size.Additions greater than one percent tend to degrade magnetic performancewhile additions less than 0.1 percent are inoperative since thesematerials are soluble to that extent even below 1,000 C.

Using the beryllium or zirconium additions, coercivity can be controlledin this family of high permeability Fe-Ni-Mo alloys in the range 65-85percent nicket and l-lO percent molybdenum remainder iron (compositionexpressed in terms of the ternary system). in these alloys themolybdenum serves to alter the electrical resistivity of the alloysthereby changing the eddy currents within the material, which currentsinfluence the switching speed. It is also believed that the molybdenuminterferes with the ordering of nickel-iron atom pairs during collingwhich would explain the insensitivity of the magnetic properties ofthese materials to cooling rate. However, since molybdenum is anonmagnetic species, magnetic alloys including it are less magnetic thanthe parent alloys thereby reducing both the Curie temperature and thesaturation magnetization. A practical limit for the disclosed alloys isof the order of percent molybdenum, A. An addition of less than 1percent is not so operative.

With the discovery that extended bodies of these materials possessed astrong 100 crystal texture (the average orientation of the crystalswhich make up the body) after heat treatment it was felt that squarenesscould be improved by making use of the magnetocrystalline anisotropy ofthese materials. If the composition is adjusted so that the anisotropyconstant K,, is positive, the 100 crystalline directions are easydirections for the magnetization (Ferromagnetism, R. M. Bozarth, D VanNostrand and Company (1951) page 563ff). Thus, the magnetocrystallineanisotropy adds to the shape anisotropy of the extended body in makingthe axis of the extended body a preferred magnetization direction. Thisleads to an improved squareness. in order to accomplish this the nickelcontent should be maintained, depending somewhat on mechanical workingand heat treatment, in the range 65-85 percent. K tends to become lesspositive with higher nickel content, (k for pure nickel is negative) butthis tendency is reduced with higher molybdenum content. FIG. 1 showsthat, within the preferred 2-8 percent molybdenum range, the highernickel alloys require a higher molybdenum content.

For those uses requiring the heat treated bodies to possess aparticularly low degree of magnetostriction in addition to possessingsquare loop properties, it is necessary to closely control the nickelcontent of the alloy. Depending upon the cold work and heat treatmenthistory of the wire, the nickel content should desirably be kept in therange, C, of 805:] percent in order to keep the weight ratio, Ni/Fe M0,in the neighborhood of 4.15. At this nickel content the squarenessconsiderations above indicate a preferred molybdenum content in therange 4-8 percent.

In addition to the above magnetically operative constituents, it is wellrecognized by those knowledgeable in the art that the addition of smallquantities of other constituents may be required by processingconsiderations or such constituents may be present as accidentalimpurities in commercial grade materials. For instance, additions ofmanganese in amounts as great as one percent of the total weight of theother constituents may be incorporated to bind any sulphur which ispresent as an impurity in commercial grades of the other constituents.Suitable alternatives are known such as magnesium and calcium. This willbe beneficial to the hot working properties of the alloy. In addition tosulphur, other accidental impurities such as silicon and phosphorus arecommonly found in commercial materials and are tolerable up to levels ofthe order of two percent of the total weight of the other constituents.Aluminum is frequently added to control oxygen content and may beincluded in an amount of up to 0.25 percent by weight.

Processing The disclosed alloys can be successfully processed intouseful device forms by working schedules including both hot and coldworking, swaging, rolling, drawing and the other working methods knownin the art. Many magnetic devices make use of round or polygonal wirebut some (e.g., the twistor) can make use of flat tapes. The twoprocesses investigated for the conversion of round wire to flat tape usel roll flattening and (2) die drawing. Although both processes areuseful they are somewhat different in both the starting material and theend result. (1) Roll flattening tends to make the tape wider than thestarting wire leaving the length essentially unchanged while (2) diedrawing results in a thin tape which tends to be essentially as wide asthe original wire diameter but longer. For instance to produce a 0.003inch wide tape one may start a roll flattening process with a 0.001 inchdiameter wire but a die drawing process with a 0.003 inch diameter wiredepending on factors such as the desired tape thickness. The texturepresent in the roll flattened and die drawn tapes after terminal heattreatment is also somewhat different. They both have a texture along thetape axis. However, roll flattened tape shows a 100 crystal plane in theplane of the tape while die drawn tape shows a 100 crystal plane in theplane of the tape. Both tapes show good squareness characteristics.

During the cold woring schedule, periodic heat treatment is necessary torelieve the working strains which degrade ductility. The heat treatmentsat the larger diameters have a relatively minor influence on the finalmagnetic properties of the resulting wires.

The two major types of heat treatment are the strand anneal, in which astrand of wire travels through a hot zone, remaining at an elevatedtemperature, T,, for a time, 1,, and the coil anneal, in which a coil ofwire is placed in a hot zone at an elevated temperature, T for a time, tThese heat treatments, which are intended primarily to effectprecipitation, usually take place at temperatures below l,O00 C. It wasfound, generally, that coil anneals at lower temperatures and longertimes are equivalent in many respects to strand anneals at highertemperatures and shorter times. In one instance, it was found that abenficial strand anneal for which T, 950 C and t, seconds was generallyequivalent to a coil anneal for which T 750 C and t 1 hour. It is a wellrecognized fact that time and temperature can often be traded off inthis way.

Some alloys were shown to benefit from a solution treatment at atemperature above l,O00 C which could take place at some intermediatewire size. This treatment tends to homogenize the alloy and dissolve anyprecipitate which has formed during the prior processing. A two hourcoil anneal at l,l00 C has been used for this purpose. Of course, themagnetic properties of the end product were most critically dependentupon the conditions of the terminal heat treatment.

Examples The alloys investigated here were vacuum melted and case inwater cooled molds which produced rods of the order of 1 inch indiameter. It was found that closer control over the relatively volatileberyllium and zirconium was obtained by keeping the temperature of themelt as low as possible. Most of the described tape samples wereproduced by the following work schedule:

A. Cold Working Schedule 1. Cut off head of ingot and machine to A; inchdiameter.

2. Homogenize at l,050 C for 2 hours (H atmosphere).

. Cold swage to 0.328 inch diameter.

. Rod anneal at 870 C for 1 hour (H atmosphere).

. Cold swage to 0.187 inch diameter.

. Rod anneal at 870 C for 1 hour (H atmosphere).

. Cold swage and cold draw to 0.063 inch diameter.

. Rod anneal at 870 C for 1 hour (H atmosphere).

. Cold draw to 0.025 inch diameter.

10. Strand anneal at 950 C by passing the wire at 24 feet per minute inN through a 6 inch hot zone Or coil anneal at temperature 750 C for l or2 hours in 90 percent N 10 percent H water quench. 11. Cold draw to 2.75mil diameter. 12. Strand anneal at temperature 0 C for 2-% sec.,

13. Cold draw to 1.28 mil diameter and roll flatten.

B. I-Iot Work Schedule 1. Cut off heat of ingot and machine to /s inchdiameter.

2. Homogenize at l,050 C for 2 hours. (H

atmosphere.)

3. Soak at 1,100 C in a H atmosphere, followed by hot swagging to inchdiameter.

4. Remaining schedule as above for cold working.

FIGS. 3, 4, 5 and 6 show the effects of the temperature of the terminalheat treatment( 2 /2 seconds strand anneal) on the magnetic propertiesof beryllium containing tapes and zirconium containing tapes which, forcomparison purposes, were all produced by the above Schedule A. Theyshow the wide range of control that can be obtained by a control of thecontent of beryllium or zirconium and the temperature of the terminalheat treatment. In FIGS. 5 and 6 the legend AP stands for as processedaccording to the above schedule. The legend ST stands for solutiontreated an additional two hours coil anneal at l,l00 C at a wire size of0.025 inch.

What is claimed is:

1. A device comprising a first elongated body consisting of a firstmagnetic material and a second elongated body consisting of a secondmagnetic material in which said second magnetic material has a remanentmagnetization at least equal to the saturation magnetization of saidfirst magnetic material and a coercivity greater than the coercivity ofsaid first magnetic material, said first magnetic material and saidsecond magnetic material being magnetically coupled to each other, saidfirst magnetic material consisting essentially of 79,58l.5 weightpercent nickel, 4-8 weight percent molybdenum with the remainder ironand as an additional portion, at least one member of the groupconsisting of beryllium and zirconium in the quantity of 0.1-1 weightpercent based on one hundred percent of said first three constituents,said first elongated body possessing a coercivity of 0.2-3 oersteds anda ratio of its remanent flux to its saturation flux of greater than 0.8,said first body and said second body having associated therewith atleast one electrically conductive path so situated that the passage ofcurrent through said path results in a magnetic flux within at least aportion of said first body and said second body.

Patent No. 3,7 1,9 Dated September 25, 1973 Inventor(s) Gilbert Y.Chin,William B. Grupen, Thomas C, Tisone It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

In the Abstract, line ll, after "80.2 percent nickel, insert "13.65percent iron,. Column 2, line 67, "wise" should be wide--. Column 3,line 32, "nicket" should be -nickel- Column 4, line 63, "100" should be---llO-- Column 5, line 31, case should be -cast-.

Signed and sealed this 19th day of February 197M.-

(SEAL) Attest:

C. MARSHALL DANN EDWARD MFLETCHERJR Commissioner of Patents AttestingOfficer FORM uscoMM-oc 60376-P69 L5. GOVERNMENT PRINTING OFFICE 2 I9690-355-33,

